26 THE STORY OF LIFE'S MECHANISM. 



universe as constant. Even if that subtile form 

 of force which we call nervous energy should 

 prove to be uncorrelated with other forms of 

 energy, the idea of the conservation of energy 

 must be changed. It is even possible that we 

 must insist that the still more subtile form of 

 force, mental force, must be brought within the 

 scope of this great law in order that it be im- 

 plicitly accepted. This law has proved itself 

 strictly applicable to the inanimate world, and 

 has then thrust upon us the various questions in 

 regard to vital force, and we must recognise that 

 the real significance of this great law must rest 

 upon the possibility of its application to vital 

 phenomena. 



No less intimate is the relation of these pro- 

 blems to the doctrine of evolution. Evolution tries 

 to account for each moment in the history of the 

 world as the result of the conditions of the 

 moment before. Such a theory loses its meaning 

 unless it can be shown that natural forces are 

 sufficient to account for living phenomena. If the 

 supernatural must be brought in here and there 

 to account for living phenomena, then evolution 

 ceases to have much meaning. It is undoubtedly 

 a fact that the rapidly developing ideas along the 

 above mentioned lines of dynamical biology have 

 been potent factors in bringing about the adop- 

 tion of evolution. Certain it is that, had it 

 been found that no correlation could be traced 

 between vital and non-vital forces, the doctrine 

 of evolution could not have stood, and even now 

 the special significance which we shall in the end 

 give to evolution will depend upon how we sue- 



